This invention relates to a method and apparatus for monitoring the burning efficiency of a furnace, and more particularly to such a method and apparatus which measures infrared radiation emitted by the flame of the furnace in at least three different wavelengths and deriving a control parameter based on the ratio of the measurements of two of the wavelengths compensated for flame length by the third measurement.
A variety of methods and apparatus have been used for monitoring combustion systems for the purpose of controlling and maximizing combustion efficiency. Some systems monitor stack gases and develop a control parameter based thereon which is used, for example, to control the air/fuel ratio. Other control systems monitor the temperature of the flame to control the input parameters. However, all of these systems are not totally satisfactory due to various factors such as the environments in which the measurements are made, complexity of the systems, response time, the problem of which burner to control when monitoring flue gases, etc.
In U.S. Pat. No. 4,179,606 a flame sensor is provided for automatically monitoring and controlling the combustion of a flame by viewing the flame in two specific wave bands and providing a ratio of the output of the radiation received from such bands to monitor and/or control the combustion. However, this approach fails to take into account the varying path lengths of the measurements through the flame which determine the prescribed ratio. In other words, varying burning rates of the fuel are not taken into account and as different fuel rates are applied to the burner the flame lengthens, and the measurements which are made on the flame will have different path lengths through the flame. Thus, the flame would have measurements taken at different penetration levels in accordance with the varying load rates. Thus, no compensation is provided for the varying amounts of fuel which are being applied and burned in the burners and full efficiency is not achieved.